The Declaration of Independence was adopted by the Second Continental Congress on July 4th, 1776. The purpose of this document was to announce that the thirteen colonies would regard themselves as sovereign states no longer under British rule. The document states that there are certain rights that all human beings have, and it is the job of the government to protect these rights. These three rights are life, liberty, and the pursuit of happiness. They are known as "unalienable rights," meaning that they cannot be taken away.
The first two rights are fairly straightforward, but "the pursuit of happiness" has caused some controversy over the years. Today, happiness is mostly known as a general positive emotion, but back in 1776, when the document was written, the common usage of happiness could have been synonymous with thriving and well-being—more closely resembling our definition of "contentment."